Two-dimensional aperture synthesis in lunar radar astronomy

It is shown that when a distant object such as the Moon or a planet is observed by a continuous wave (c. w.) radar employing a single aerial, components of the two-dimensional Fourier transform of the target’s radar brightness distribution may be obtained by computing the autocorrelation function of the complex amplitude of the returned signals. When the motion of the radar relative to the target is suitable, sufficient components may be measured to allow the two-dimensional radar brightness distribution to be recovered. This process has been carried out for the Moon. Observations have been made with a radar operating at a wavelength of 73 cm transmitting circularly polarized signals and receiving the orthogonal polarization. Reduction of the data has enabled an unambiguous two-dimensional map of the lunar radar brightness distribution to be constructed with an angular resolution of 3'.